MIPS: lantiq: Make reset_control_ops const

The reset_ops structure is never modified. Make it const.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: John Crispin <john@phrozen.org>
Cc: linux-mips@linux-mips.org
Cc: kernel@pengutronix.de
Patchwork: https://patchwork.linux-mips.org/patch/12619/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>